Read this lawsuit: Tether only has $50 mill and their wires have been frozen by Wells Fargo since March 2017. So the remaining $600 mill tokens are backed by nothing.
That was filed back in April when there were only $50 million Tether in existence: https://coinmarketcap.com/currencies/tether/ Also, the money that's supposedly backing Tether is in Taiwanese banks, not Wells Fargo, and their problem with Wells Fargo should only affect international wires.
http://article78againstnydfs.com/docs/317-cv-01882-BitfinexC...